Keyed alarm



June 14, 1966 Filed Aug. 6, 1962 G. CAPRIO 3,256,515

KEYED ALARM z Sheets-Sheet l Q5/2940 L. Cfiv /Z/o INVENTOR- June 14, 1966 G. L. CAPRIO I 3,256,515

KEYED ALARM Filed Aug. 6, 1962 2 Sheets-Sheet 2 F IG. 3 V

| I I 206: I

l I I Gael-7L L CAPE/O 204 INVENTOR.

United States Patent ware Filed Aug. 6, 1962, Ser. No. 215,213 Claims. -(Cl- 340-171) This invention relates to a keyed alarm system and more particularly to a system for providing a positive alarm in response to a monotonic signal after a time delay which may be selectively variable over a wide range.

This invention finds application in alarm systems such as those to be used for radio transmission for reception by the general populace. It may be included in a radio receiver which is to be maintained on an alarm stand-by basis pending the receipt of a particular signal and following which the receiver operates in conventional mode. It is necessary in order to make certain that only the intended signal will serve to actuate the system. Furthermore, it must be immune to noise signals and improvident occurrences which might otherwise trigger the same. In

addition, it must be adapted to be maintained in a stand-by condition preferably in either a fixed or portable state. Thus the electronic circuitry meeting the foregoing demands embodies specific cooperation between various elements therein which lead to a new combination not heretofore known in the art.

In accordance with the present invention, a keyed alarm circuit is provided which is responsive to a component of a received signal of monofrequency character if and only if such component is sustained for a time interval of substantial duration. More specifically, there is provided a sensing circuit preferably including a tuned electromechanical element responsive only to a component of a received signal of said monotonic character. There further is provided a normal quiescent utilization circuit. A circuit is then connected between the sensing circuit and the utilization circuit which includes a switch means and a time delay circuit for applying to the switch means an actuating signal from the sensing circuit. Connected to said time delay circuit is a reset control. The period of time delay circuit is of substantial length, with the period of the reset control being operative substantially instantaneously.

In a more specific aspect, a first circuit is provided for applying to the electromechanical element an actuating force which varies in accordance with variation with the multicomponent signal. A control circuit including a capacitor and a voltage source is provided for normally maintaining a charge on the capacitor. An actuating circuit is connected between the control circuit and the electromechanical element for initiating discharge of the capacitor and for continuing said discharge as long as the electromechanical element is actuated. An alarm is provided which is responsive to a change in the charge on the capacitor at a predetermined fraction of the initial charge. A charging circuit is provided for the capacitor which is completed upon cessation of actuation of the electromechanical element. The charging circuit has a time constant very small compared with the time constant of the control circuit.

For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a schematic diagram of one embodiment of the invention;

FIGURE 2 illustrates a modification of the invention in which two units are employed; and

Patented June 14, 1966 FIGURE 3 is an isometric view, partly in section, showing one embodiment of the invention.

Referring now to FIGURE 1, there is illustrated in schematic diagram form a radio receiver in which the alarm system of the present invention is included. The example of FIGURE 1 is a transistorized AM receiver, battery powered and operable either in a stand-by alarm condition or in a broadcast reception condition.

More particularly, a receiving antenna 10 is provided at the input of the signal channel in which a mixer-oscillator stage 11 includes a transistor 11a. Tuning capacitors 10a and 111; are mechanicallycoupled as by link 110 so that the local oscillator including transistor 11a may be made to track the signal to which the circuit including the antenna 10 is tuned.

An I.F. signal is then transmitted by way of the LF. transformer 12 to the first I.F. amplifier 13. The signal is then transmitted by way of IF. transformer 14 to the second LF. stage 15.

A third LF. transformer 16 is connected atits output to a demodulator 17, including diode 17a, which provides an audio output signal which is developed across a capacitor 170. A resistor 17b is connected between diode 17a and a volume control 172. A capacitor 17d is connected across the control 17e.

The variable tap on the volume control 17 e is connected to terminal 18 of a first section 19a of a multisection switch section and audio sections of the receiver are powered from. a battery 30, the negative terminal of which is connected to bus 31 by way of the on-oif switch 28 and the relay 99. The positive terminal of battery 30 is connected to a ground reference terminal or bus 32.

For broadcast reception, the volume control .17e pro vides adjustment to the desired audio output level at speaker 25. However, applicant has provided an alarm .unit particularly suitable for use on a standby basis as to be continuously responsive to a signal of particular character appearing at the second terminal 20 of switch section 19a which is conected for maximum gain. Terminal 20 is connected through resistors 17b and 27 to the oathode of the detector 17a. By this means the maximum signal output is applied by way of switch section 19a to the audio amplifier. In the stand-by condition it will be noted that the switches 19b and 19!: disconnect the amplifier 22 from the speaker 25wand connect it to a resonant reed relay coil of the alarm unit. Reed contact 62 is connected to ground. The vibrating reed 63 actuated by and upon energization of coil 60 is connected by way of resistor 64 and the RC networwk 65 to the bus 31.

The battery 30 is trickle-charged from a power supply circuit including a plug which may be connected to a power line as by a convenience outlet to apply alternating current to the power supply transformer 7'1. The secondary winding of the transformer 71 is connected at itscentral terminal to ground and .at its extremities to rectifiers 72 and 73. The anodes of the rectifiers 7-2 and 73 are connected together and to a capictor 74. A voltage regulator 75 is connected at its output to the negative terminal of battery 30 to maintain a trickle charge on the battery 30. It will be noted that battery power is applied to the bus 3 2 from battery 30 only when the switch 19d is closed.

The RC circuit -65- is connected by way of resistor to the base of a transistor 81 whose emitter is connected to the bus 31. The collector of transistor 81 and the base of transistor 83 are interconnected. The emitter of transistor 83 is connected by way of diode 84. to the bus 3 1 and, by way of resistance 85, to the ground bus 32.

Capacitor 87. connects the collector of transistor 83 to the ground bus 3-2. Series resistances 88 and 89 parallel the capacitor 87 with the juncture between resistances 88 and 89 being connected to the base of transistor 90 and, by way of capacitor 91, to the bus 3 1. The collector of transistor 90 is connected to the bus 311. The emitter is connected by way of resistance 92 to the bus 32 and to the emitter of a transistor 93. The base of transistor 93 is connected by way of resistance 94 to the bus 32 and by way of variable resistance 95 and resistance 96 to the bus 31. The collector of transistor 93 is connected by way of resistance 97 to the bus 31 and also to the base of transistor 98.

The transistor 98 isconnected in series with a relay coil 99. More particularly, the emitter of transistor 98 is I connected to the bus by way of resistor 96 and the collector is connected to one terminal of the coil 99. The other terminal of the latter coil is connected to the bus 32.

The relay coil 99 serves to actuate the relay armature 99a which is connected to the switch 28. Terminal 9% is connected to bus 31 and the other terminal 99c is connected by way of resistance 100 to the collector of transistor 98 and to a buzzer alarm unit 101 which includes a vibrating contact 102 and an energizing coil 103.

In order to provide desired operation, the resonant reed 63 is sharply tuned, vibrating only when an alternating current signal of sufiicient amplitude and at the exact frequency to which the reed is tuned is applied across the terminals of coil 60. When the reed 63 vibrates, it makes intermittent contact to close the circuit from ground terminal 62 to the RC circuit 65. The intermittent contact thus made serves to apply intermittent pulses to the circuit 65 wherein they are integrated. The system response is keyed as to frequency and produces a DC. voltage which is applied through resistance 80 to the base of transistor 81. Resistance 80 serves to limit the base current of the transistor 81. Transistor 81 is a switching transistor which is normally non-conducting, i.e., when no alarm signal is present in the output of the receiver. Resistance 82 is the collector load resistor for transistor 81. However, when a signal is received having the precise frequency to which the reed 63 is tuned and is of suflicient amplitude to cause the reed to vibrate, a voltage is then applied to the base of the transistor 81. This voltage is established almost instantaneously across the capacitor 654 in network and when the signal is removed, the DC. voltage on capacitor in circuit 65 collapses almost instantaneously. When a DC. voltage is present across the capacitor 65a, the transistor 81 is switched from nonconducting to a conducting condition. Resistance and the diode 84 serve to maintain a bias voltage for the transistor 83. This causes the transistor 83 to be nonconducting when the transistor 81 is conducting. The series resistors 88 and 89 comprise the collector load resistance for transistor 83.

When no signal of frequency to which the reed 63 is tuned is present, the transistor 81 is cut off, permitting current to flow through resistance 82 and the base-emitter junction of transistor 83. This places transistor 83 in a highly conducting or saturated state. When transistor 83 is saturated, the low resistance represented thereby and by the diode 84 permits capacitor 87 to charge rapidly to the full voltage drop across the resistances 88 and 89. However, when the tone to which the reed 63 is tuned is present, the transistor 81 becomes saturated. This immediately cuts off the transistor 83. Upon cutotf in transistor 83, the capacitor 87 is allowed to discharge at a relatively slow rate through resistances 88 and 89. Any time that the alarm signal is removed or interrupted, capacitor 87 will be recharged almost instantaneously.

4 Transistors 90 and 93 along with resistances 92, 94, 95,

96 and 97 constitute a direct current diiierential amplifier which is responsive to the voltage across capacitor 87. The setting of the resistance determines the point along the RC discharge characteristic of the capacitor 87 at which the transistor 98 will be switched from a normally non-conducting state to a conducting state.

To illustrate alarm use of the system, note that conelrad transmission of a general alarm signal is at a broadcast frequency in the form of a 1000 cycle tone maintained for fifteen seconds. The resistance 95 is set such that the transistor 98 will begin to conduct after a preset delay, preferably of the order of about ten seconds. This time delay may be set from two seconds up to as much as thirty seconds by selection of the time constant of circuit 87, 88, 89.

Transistor 98 serves to operate the relay coil 99. The relay coil 99, when energized, moves armature 990 from contact 99b to contact 990, completing a circuit to a buzzer 101 from battery 30. The relay coil 99, or locking means, is thereafter maintained energized by flow of current through resistance 100, holding the relay closed so that the buzzer 101 will continue to operate after the trigger signal is removed. Once the contacts of relay 99 have been actuated, the buzzer 101 will continue to operate until a power connection is interrupted. Thus, with the receiver in an alarm stand-by condition, the reception of a 1000 cycle tone signal will energize the buzzer 101 only if the 1000 cycle signal is maintained for the preset period of the circuit 87, 88, 89, and 95. Once the buzzer is energized, a listener will be immediately warned that an alert is in etfect. Momentary opening of switch 28 will remove the power from the alarm circuit, stopping the buzzer. Switch 19 may then be actuated to change the receiver circuit from its alarm-standby to its normal reception state wherein the audio circuit of the receiver is connected by way of the volume control 17e to the detector circuit, and the speaker 25 is connected to the output of the amplifier 22.

It will be noted that terminal 104 of the buzzer 101 is connected by way of resistance 105 to the alarm terminal 106 of the switch section 190. When the switch 19 is in the alarm position, the energizing signal applied to the buzzer coil 103 is also applied to the speaker 25 so that a distinctive audible signal will be produced by the speaker 25. It will be noted that the speaker 25 is connected to ground by way of a phone jack 107. This jack permits the connection to a circuit, such as circuit 108, leading to a second speaker 109 so that the system may operate a local speaker and one or more remote speakers.

From the foregoing it will be seen that the RF. as well as the audio section of the receiver together with the alarm circuit are powered from battery 30. Battery 30 is maintained in a charged condition by use of the rectifier circuit leading from the power plug 70. The system, by this means, is assured of proper operating voltage and may be maintained on a stand-by basis for long periods ready to receive an alarm should any signal corresponding to the frequency of the reed 63 be received. Upon receipt of the signal, the alarm is energized. The receiver may then be switched to a broadcast-receiving condition. It may be maintained in the same physical location with the plug '70 maintaining connection to a power circuit.

Alternatively, if the power circuit should be dead orshould fail or if it is desired to move the receiver to a different location following reception of an initial alarm, the battery is in a fully charged condition for assuring maximum service as a portable unit at a time of greatest need. Note that triggering of the alarm disconnects the system from the battery 30 except the alarm 101. Battery power thus is required only to power the alarm 101 and the speaker 25 after reception of a keyed signal.

Thus, there is provided a combination which includes a receiver system having a tuned element responsive only circuit are mounted in a second chassis which is adapted to be wall mounted in contact with a convenience outlet or otherwise supplied with power for maintaining the battery and the receiver in a charged state. bodiment of the invention shown in FIGURE 1, the switch 19 is automatically actuated by insertion of the chassis into the holder and by removal therefrom. Upon insertion, the circuit from the power supply to the battery is completed as in the circuit from the battery to the alarm circuitry.

More particularly, in FIGURE 2 the receiver portion of the system is housed in a first unit X with the alarm and the power supply system housed in a unit Y (shown dotted). It will be noted that the battery 30 is housed in the unit X but it is so connected that it must be charged from unit Y. A multi-terminal plug including contacts A-D is provided for connecting the unit X to the unit Y. More particularly, the contacts A-A serve to connect the alarm terminal on the switch section 1912 from speaker to the driving coil 150 of a tuned reed device. Terminals BB connect the bus 32 in unit X to the bus 32 in unit Y. The terminals CC connect the power supply 151 to the negative terminal of battery 30. The terminals DD connect the bus 31 and the negative terminals of battery to the bus 31' in unit Y.

It will be noted that the terminals C and D in unit X are shorted together so that the alarm unit Y will be energized only when connected to the unit X.

The alarm circuit of FIGURE 2 connected to the reed relay 150 may be employed as a separate unit such as illustrated by the unit Y of FIGURE '2 or it may be employed in substitution for the more complex alarm circuit of FIGURE 1. The alarm circuit of FIGURE 2 is preferred in that it is less complex and provides stability that is not present in the alarm circuit of FIGURE 1. More particularly, in accordance with FIGURE 2, the contact 153 associated with the tuning fork 154 is c011- nected by way of a resistor 155 to the base of a transistor 156. The base is also connected by way of an RC network 157 to the bus 32. The emitter electrode of transistor 156 is connected to bus 31'. The collector of transistor 156 is connected to the bus 32' by Way of the capacitor 157 and variable resist-or 158. Elements 157 and 158 form a pararallel circuit, the time constant of which determines the switching characteristics of the sensing system. The collector of transistor 156 is connected by way of resistor 160 to the base of a transistor 162. The base of transistor 162 is also connected by way of resistor 1'64 and 165 to'a parallel circuit including resistor 166 and a thermistor 167 which are connected to the bus 32'. The juncture between resistors 164 and 165 is connected by way of resistor 170 to the emitter electrode of transistor 171, by way of resistor 172 to the bus 31 and by way of diode 173 to bus 32'. The emitter electrode of transistor 162 is connected to the bus 32'. The collector electrode of transistor 162 is connected. to the bus 31 by way of a resistor 175 and to the base of transistor 171. The collector of transistor 171 is connected by way of a relay coil 17-7 to the bus 31. It is also connected by Way of resistor 178 to the normally open contact associated with relay 177 and to the arm 179 of a buzzer 180. The normally closed terminal associated with relay 180 is connected in series with the relay coil and thence to the bus 31'. The armature of relay 177 is connected by way of conductor 181 to the bus 31.

In operation when a signal to which the reed 154 is In this emtuned is applied to the terminals AA and wit-h the buses 31 and 32' energized, the transistor 156 will promptly be rendered non-conductive whereupon the charge on capacitor 157 will begin to leak off. The time required for the voltage on'the base of transistor 162 to become sufficiently low to permit conduction will be controlled by the setting of the variable resistor 158. The time constant is somewhat controlled by the parallel circuit including resistors 160, 164, 165, 166 and 167. The thermistor 167 serves to compensate for variations with temperature of the base-emitter forward conduction knee of the transistor 162. As well-known, the barrier potential of a transistor varies inversely with temperature so that in order to incorporate the desired stability as to the time at which the circuit of FIGURE 2 will actuate the alarm following the onset of the monotonic signal, it was found desirable to provide such compensation.

As transistor 162 begins conduction, transistor 171 also begins to conduct, thereby closing the relay 177. This applies power from bus 32' through the buzzer coil 180. The latter circuit is repeatedly broken by actuation of the armature 179. At the same time the circuit by way of resistor 178 maintains the relay coil 177 energized so that the remainder of the circuit may be restored to its stand-by condition upon termination of the signal on coil 150. Thebuzzer 180 will then remain energized until manually stopped or otherwise rendered inoperative.

It will be noted that in the foregoing system the systems X and Y are to be mated for stand-by operation. The receiver X may, upon sounding of an alarm, be removed from'syste-m Y and.then be employed as a conventionally designed portable radio receiver but with the assurance that at the outset the battery 30 is in a fully charged condition. Thus, not only is there provided a reliable stand-by unit, but upon the occurrence of an alarm signaled by the stand-by unit, the receiver unit will then be fully operative for receipt of voice information as may be desired. The system, therefore, is dependent upon power for charging as by way of the power supply 151 only until the time that a major requirement for the use of the alarm-signaling system may come int-o being.

' In FIGURE 3 the-re is illustrated one embodiment in which the receiver unit X and the alarm system Y are physically encased so that the unit Y will receive the unit X in a manner conveniently adapted for use in its stand-by state. More particularly, a housing 200 is provided with a speaker enclosure 201, a volume control 202 and'with an antenna-handle element 203. The unit X may be of a form of a small transistorized radio frequency receiver. In the lower end of the receiver X there is a four terminal plug having terminals corresponding with terminal-s A-D of unit X, FIGURE *2. A mating plug is provided in unit Y so that the connections AA- DD can be completed by insertion of the unit X into the nest in the unit Y.

Unit Y is provided with male electrical terminals on the rear face thereof for insertion into a convenience outlet such as on the unit 204. The unit Y would be connected with the upper of the two outlet receptacles on the convenience outlet 204 leaving the lower one, the

outlet 205, available for normal use. The switches 19a- 19d of FIGURE 1 are actuated by a push bar 206 mounted in the bottom of the nest in the holder Y and adapted to be inserted into a slot in the bottom of the unit X to engage the structure rep-resented by linkage 19 of FIG- URE 1. Upon energizing the alarm, signaling the receipt of a keyed tone by the unit Y, the unit X will be lifted from its nest. A spring 19e incorporated in unit X and linked as shown in FIGURE 1 will automatically switch the receiver to the broadcast-receiving condition.

The relationship between the alarm unit of FIGURE 1 and the receiver system and control circuits for modifying one with respect to the other are described and claimed in an application of Roger L. Weber, filed con- (b) a control circuit including a capacitor, a transistor and a voltage source connected in series,

(c) means for maintaining said transistor in a normally conducting state for charging said capacitor to the voltage of said source,

((1) a discharge path connected across said capacitor having a relatively long time constant,

(e) a voltage sensing circuit connected across said capacitor, for sensing the voltage across said capacitor,

(f) an alarm circuit including normally open switch means and an alarm element connected across said source,

(g) a circuit connected between said voltage sensing circuit and said normally open switch means for closing said normally open switch means when the voltage across said capacitor reaches a predetermined discharge level, and

(h) a circuit forming a part of the control circuit having a time constant very short compared with the time constant of said discharge path for terminating and re-establishing conduction in said transistor instantaneously with the onset and termination, respectively, of the application to said filter of a signal component to which said filter is tuned.

2. The combination set forth in claim 1 in which locking means is provided for maintaining said alarm element energized following each actuation thereof.

3. An alarm circuit which comprises:

(a) a sharply tuned electromechanical filter,

(b) means for applying to said filter an actuating force which varies in dependence upon variations in amplitude and frequency of the components of an input signal,

(c) a control circuit including a voltage source, a capacitor and the collector emitter path of a first transistor connected in series with said voltage source,

(d) a long time constant discharge path for said capacitor, said path having elements providing a predetermined time constant and said elements being connected across said capacitor,

(e) a bias circuit connected to the base of said transistor and to said filter having a very short time constant for normally maintaining said transistor conductive and for rendering said transistor non-conductive upon actuation of said filter,

(f) a voltage sensing circuit including a second transistor connected in its collector emitter path across ing its collector emitter path connected in series with an alarm element and to said source for energizing said alarm element when said third transistor is rendered conductive.

4. The combination set forth in claim 3 in which locking means is provided for maintaining said alarm element energized following each actuation thereof.

5. An alarm circuit which comprises:

(a) a sharply tuned electromechanical filter,

(b) means for applying to said filter an actuating force which varies in dependence upon variations in amplitude and frequency of the components of an input signal,

(c) a control circuit including a voltage source, a capacitor and the collector emitter path of a first transistor connected in series with said voltage source,

(d) a long period discharge path for said capacitor, said path having elements providing a predetermined time constant and said elements being connected across said capacitor,

(e) a bias circuit connected to the base of said transistor and to said filter having a very short time constant for normally maintaining said transistor conductive and for rendering said transistor nonconductive upon actuation of said filter,

(f) a voltage sensing circuit including a second transistor connected in its collector emitter path across said source and connected at its base to said first transistor for sensing the voltage across said capacitor,

(g) a third transistor normally non-conductive and connected at its base to said first transistor and having its collector emitter path connected in series with an alarm element and to said source for energizing said alarm element when said third transistor is rendered conductive, and

(h) a compensating network connected to one terminal of said source, to the base of said second transistor and to one of the collector and emitter terminals of said third transistor for compensating variations in temperature in said alarm circuit.

References Cited by the Examiner UNITED STATES PATENTS 2,388,576 11/1945 Seeley et al. 325-364 2,993,991 7/1961 Lundahl 325-392 X 3,009,059 11/1961 Stratton et a1 325-364 FOREIGN PATENTS 526,230 9/1940 Great Britain. 855,627 11/ 1958 Great Britain.

NEIL C. READ, Primary Examiner.

,, P. XIARHOS, Assistant Examiner. l) 

1. THE COMBINATION WHICH COMPRISES: (A) A SHARPLY TUNED ELECTROMECHANICAL FILTER BEING TUNED TO A MONOTONIC SIGNAL COMPONENT WHICH CEASES TO BE PRODUCED AFTER A PREDETERMINED TIME INTERVAL, (B) A CONTROL CIRCUIT INCLUDING A CAPACITOR, A TRANSISTOR AND A VOLTAGE SOURCE CONNECTED IN SERIES, (C) MEANS FOR MAINTAINING SAID TRANSISTOR IN A NORMALLY CONDUCTING STATE FOR CHARGING SAID CAPACITOR TO THE VOLTAGE OF SAID SOURCE, (D) A DISCHARGE PATH CONNECTED ACROSS SAID CAPACITOR HAVING A RELATIVELY LONG TIME CONSTANT, (E) A VOLTAGE SENSING CIRCUIT CONNECTED ACROSS SAID CAPACITOR, FOR SENSING THE VOLTAGE ACROSS SAID CAPACITOR, (F) AN ALARM CIRCUIT INCLUDING NORMALLY OPEN SWITCH MEANS AND AN ALARM ELEMENT CONNECTED ACROSS SAID SOURCE, (G) A CIRCUIT CONNECTED BETWEEN SAID VOLTAGE SENSING CIRCUIT AND SAID NORMALLY OPEN SWITCH MEANS FOR CLOSING SAID NORMALLY OPEN SWITCH MEANS WHEN THE VOLTAGE ACROSS SAID CAPACITOR REACHES A PREDETERMINED DISCHARGE LEVEL, AND 